Metallized ceramic substrate having smooth plating layer and method for producing the same

Abstract

A metallized ceramic substrate having a smooth plating layer comprises a ceramic substrate containing aluminum nitride as a main component; a tungsten- and/or molybdenum-based metallized layer formed on at least one face of the ceramic substrate; and a nickel-based plating layer formed on the metallized layer wherein the plating layer has a thickness of not greater than 2 mu m and a surface roughness (Ra) of not greater than 2 mu m. Alternatively, the plating layer on the ceramic substrate may comprise a first nickel-based plating layer having a thickness of not greater than 2 mu m and a second gold-based plating layer having a thickness of not greater than 1 mu m wherein the gold-based plating layer has a surface roughness (Ra) of 2 mu m or less. These metallized substrates are produced by applying a metallizing paste containing tungsten and/or molybdenum onto a green aluminum nitride ceramic substrate, flattening the metallizing paste layer, firing the metallizing paste-coated ceramic substrate, and forming the plating layer or layers.

What is claimed is: 
     
       1. A metallized ceramic substrate having a smooth plating layer, said metallized ceramic substrate comprising: a ceramic substrate comprising aluminum nitride as a main component and prepared from a green ceramic substrate with a Rockwell hardness of 100 HRS or lower;   a metallized layer formed on at least one face of said ceramic substrate wherein the metallized layer comprises at least one member selected from the group consisting of tungsten and molybdenum as a main component; 0.1 to 15 parts by weight of a glass component per 100 parts by weight of tungsten and molybdenum wherein the glass component is at least one selected from the group consisting of CaO, MgO, Al 2  O 3 , SiO 2 , B 2  O 3 , ZnO, PbO, oxides of rare earth metals, compounds which yield the above listed oxides by firing, and complex compounds thereof; and 0.001 to 5 parts by weight of an additive per 100 parts by weight of tungsten and molybdenum wherein the additive is at least one selected from the group consisting of nickel, iron, cobalt, their oxides, and their alloys; and   a plating layer formed on said metallized layer and comprising nickel as a main component, said nickel plating layer having a thickness of not greater than 2 μm and a surface roughness Ra of not greater than 2 μm.   
     
     
       2. A metallized ceramic substrate having a smooth plating layer, said metallized ceramic substrate comprising: a ceramic substrate comprising aluminum nitride as a main component and prepared from a green ceramic substrate with a Rockwell hardness of 100 HRS or lower;   a metallized layer formed on a at least one face of said ceramic substrate wherein the metallized layer comprises at least one member selected from the group consisting of tungsten and molybdenum as a main component; 0.1 to 15 parts by weight of a glass component per 100 parts by weight of tungsten and molybdenum wherein the glass component is at least one selected from the group consisting of CaO, MgO, Al 2  O 3 , SiO 2 , B 2  O 3 , ZnO, PbO, oxides of rare earth metals, compounds which yield the above listed oxides by firing, and complex compounds thereof; and 0.001 to 5 parts by weight of an additive per 100 parts by weight of tungsten and molybdenum wherein the additive is at least one selected from the group consisting of nickel, iron, cobalt, their oxides, and their alloys; and   a first plating layer comprising nickel as a main component and formed on said metallized layer, said nickel plating layer has a thickness of not greater than 2 μm; and   a second plating layer comprising gold as a main component and formed on said first plating layer, said gold plating layer having a thickness of not greater than 1 μm and a surface roughness Ra of not greater than 2 μm.   
     
     
       3. A method for producing a metallized ceramic substrate of claim 1 having a smooth plating layer, said method comprising: applying a metallizing paste onto at least one face of a green ceramic substrate comprising aluminum nitride as a main component and having a Rockwell hardness of 100 HRS or less wherein the metallizing paste comprises at least one member selected from the group consisting of tungsten and molybdenum as a main component; 0.1 to 15 parts by weight of a glass component per 100 parts by weight of tungsten and molybdenum wherein the glass component is at least one selected from the group consisting of CaO, MgO, Al 2  O 3 , SiO 2 , B 2  O 3 , ZnO, PbO, oxides of rare earth metals, compounds which yield the above listed oxides by firing, and complex compounds thereof; and 0.001 to 5 parts by weight of an additive per 100 parts by weight of tungsten and molybdenum wherein the additive is at least one selected from the group consisting of nickel, iron, cobalt, their oxides, and their alloys;   placing a plate having a surface roughness Ra of not greater than 0.7 μm onto said substrate and flattening said metallizing paste-applied face under pressure;   firing said substrate in a non-oxidizing atmosphere; and   forming a plating layer comprising nickel as a main component onto the metallized layer, said plating layer having a thickness of not greater than 2 μm and a surface roughness Ra of not greater than 2 μm.   
     
     
       4. A method in accordance with claim 3, wherein said flattening process is implemented by applying a pressure of not less than 15 kg/cm 2  onto said metallizing paste-applied surface of said green ceramic substrate at a temperature of not lower than 15° C. 
     
     
       5. A method for producing a metallized ceramic substrate of claim 2 having a smooth plating layer, said method comprising: applying a metallizing paste onto at least one face of a green ceramic substrate comprising aluminum nitride as a main component and having a Rockwell hardness of 100 HRS or less wherein the metallizing paste comprises at least one member selected from the group consisting of tungsten and molybdenum as a main component; 0.1 to 15 parts by weight of a glass component per 100 parts by weight of tungsten and molybdenum wherein the glass component is at least one selected from the group consisting of CaO, MgO, Al 2  O 3 , SiO 2 , B 2  O 3 , ZnO, PbO, oxides of rare earth metals, compounds which yield the above listed oxides by firing, and complex compounds thereof; and 0.001 to 5 parts by weight of an additive per 100 parts by weight of tungsten and molybdenum wherein the additive is at least one selected from the group consisting of nickel, iron, cobalt, their oxides, and their alloys;   placing a plate having a surface roughness Ra not greater than 0.7 μm onto said metallizing paste-applied face of said green ceramic substrate and flattening said metallizing paste-applied face under pressure;   firing said substrate in a non-oxidizing atmosphere;   forming a first plating layer comprising nickel as a main component onto the metallized layer, said first plating layer having a thickness of not greater than 2 μm; and   forming a second plating layer comprising gold as a main component onto the said first plating layer, said second plating layer having a thickness of not greater than 1 μm and a surface Ra of not greater than 2 μm.   
     
     
       6. A method in accordance with claim 5, wherein said flattening process is implemented by applying a pressure of not less than 15 kg/cm 2  onto said metallizing paste-applied surface of said green ceramic substrate at a temperature of not lower than 15° C.